1. Field of the Invention
The present invention is generally related to a cordless lanyard system and, more particularly, to a cordless lanyard system that generates and senses an e-field magnitude to determine whether or not an operator of a marine vessel is in a proper position relative to the helm station of the vessel.
2. Description of the Related Art
Various devices and procedures have been developed to assure that an operator of a marine vessel is in a proper position at the helm of the vessel. These systems vary from simple cords attached between the operator and a switch to turn off a marine engine when the operator leaves the helm station and more complex systems that use infrared technology to sense the presence of the operator at the helm station. Various devices, using e-field technology, have been developed to sense the presence of an object within certain specified detection zones.
United Kingdom Patent Application GB 2286247, which was filed by Gershenfeld on Jan. 24, 1995, describes a capacitive position detection system. A sensor for monitoring a characteristic of an object, for example, its position is described. The sensor includes an electrode pair and a signal generator connected to pass a displacement current between the electrodes. Changes in the position or other monitored characteristic of the sensed object modify the displacement current and sensing of that current thus provides an electrical indication of the sensed changes. A multiple electrode pair system can be used to monitor the position of an object with improved accuracy by sensing the displacement currents between multiple pairs of electrodes.
International Application Publication Number WO 97/35738, which was filed by Kithil et al. on Mar. 7, 1997, describes a motor vehicle occupant sensing system. A roof-mounted passenger position sensor array of capacitive coupling passenger position sensors is provided to determine position and motion of a passenger by analysis of distances of the passenger to the various sensors of the array and analysis of the changes of the distances with time.
U.S. Pat. No. 5,019,804, which issued to Fraden on May 28, 1991, describes an apparatus and method for detecting movement of an object. A sensor electrode is capacitively coupled to the environment. Electric charges carried by surrounding objects induce corresponding electric charges on the sensor electrode. A high input impedance circuit senses changes in charge on the electrode and provides a first varying signal indicative of that change. A second circuit compares the first signal against a threshold level and provides a second signal indicative of the movement.
U.S. Pat. No. 5,936,412, which issued to Gershenfeld et al. on Aug. 10, 1999, describes a method for resolving presence, orientation and activity in a defined space. It utilizes at least two electrodes proximate to the space to be observed. A characterization of the position and orientation is obtained by providing a pattern of measurement clusters each associated with a position and an orientation. An AC signal is applied to one electrode and the current measured from the electrode to any other electrodes included in the system and which are effectively connected to the ground return of the AC-coupled electrode. A person to be sensed intercepts a part of the electric field extending between the AC-coupled sending electrode and the other receiving electrodes, the amount of the field intercepted depending on the size and orientation of the sensed person.
U.S. Pat. No. 6,329,913, which issued to Shieh et al. on Dec. 11, 2001, describes a passenger detection system and method. The system utilizes an oscillation circuit that causes an antenna electrode to emit an electric field that is disrupted by the electrical characteristics of an object placed on the seat. This disruption alters the current and phase of the signal in the antenna electrode. By comparing the current flowing in the antenna electrode and/or the difference between the phase of the signal in the antenna electrode and the oscillation circuit output signal with predetermined threshold values, it is possible to detect the presence of a passenger in a reliable and inexpensive manner.
U.S. Pat. No. 6,450,845, which issued to Snyder et al. on Sep. 17, 2002, discloses a passive occupant sensing system for a watercraft. A thetherless occupant detector system uses an infrared sensor and a monitor circuit that provides a deactivation signal to an engine control unit or other control mechanisms in the event of an operator of the marine vessel leaving a preselected control position at its helm. The infrared sensor provides an output signal that is generally representative of the heat produced by an occupant within the control position of a marine vessel. The monitor circuit reacts to a sudden decrease in this heat magnitude and provides a deactivation signal in response to detecting this sudden decrease. The deactivation signal provided by the monitor circuit can be received by an engine control unit which then, in turn, deactivates a marine propulsion system. Alternatively, the deactivation signal itself can cause a deactivation of the marine propulsion system.
U.S. Pat. No. 6,509,747, which issued to Nagai et al. on Jan. 21, 2003, describes an apparatus for detecting seated condition. The apparatus detects whether a passenger is seated on a seat and the location of the passenger if seated. In the apparatus for detecting seated condition, antenna electrodes are provided in the inside of the seat so that the electric field generates between the ground and the antenna electrodes. A detecting circuit detects a first output of the electric field in a case that a passenger is not seated and a second output of the electric field in a case that a passenger is seated.
U.S. Pat. No. 6,661,115, which issued to Lester on Dec. 9, 2003, describes a conductive e-field occupant sensing system. The apparatus is intended for sensing size and locations of a vehicle occupant and includes a conductor that is electrically coupled to a voltage signal generator and disposed within the seat of the vehicle. The conductor generates a periodic electric field. A plurality of sensor electrostatic antennas is disposed adjacent the roof and is capable of sensing at least a portion of the electric field. A detection circuit determines the size and location of a vehicle occupant based upon an amount of the electric field incident on each sensor electrostatic antenna.
U.S. Pat. No. 6,825,765, which issued to Stanley et al. on Nov. 30, 2004, describes an occupant detection system. It comprises a weight sensor and an electric field sensor, each operatively coupled to a seat. The electric field sensor generates an electric field from at least one electrode in the seat bottom of the seat, provides for generating a response to an influence of the occupant thereupon, and is adapted to provide for discriminating from the response a seated infant or child seating condition from another seating condition.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
An article, titled “E-field Evaluation Module” appeared in the June 2003, Issue 155, addition of Circuit Cellar which is available on the Internet. It describes a Motorola product that is adaptable to various sensor systems and uses an e-field to determine the presence of various objects within a defined zone.
A contest, using e-field sensors, is described on the Internet at a website identified as “http://www jandspromotions.com/efield2003/. One of the entries in the Motorola e-field sensor contests describes an electronic whoopie cushion deux that uses an e-field sensor. The system reacts to a person sitting on a flat device places on or under a cushion of a chair. When a human being is sensed, a sound emanates from the system.
It would be significantly beneficial if an occupant sensing system could be provided for a marine vessel in which the system is not dependent on surrounding the occupant with various sensors above and below the monitored position. It would also be significantly beneficial if the system could monitor the position of the occupant whether the occupant is sitting or standing within the appropriate detection zone. Furthermore, it would be significantly beneficial if an occupant detection system could be provided which is not overly sensitive to moisture and other changes in the environment within which the system is used. It would be further beneficial is such a system could be self-calibrating in nature.